1. Field of the Invention
The present invention relates to a reflecting surface of photometer, colourmeter and the like, a reflecting surface widely usable as a working white standard and a method for producing the surface.
2. Description of the Prior Art
Conventionally, MgO smoked surface has often been used as a working standard for spectral reflectance in spectromesuring, spectrophotometer, etc. Said MgO smoked surface has excellent spectrophotomeric characteristics such as a high spectral reflectance of the smoked surface, low selectivity of wavelength in visible area and similarity to the perfect diffusing surface.
However, the MgO smoked surface has extremely low mechanical strength, lacks durability and has great limitation in its production.
Many attempts have been made to obtain a working white standard to be substituted for said MgO smoked surface, and a white coating surface obtained by spray coating method has been generally utilized in case of a large reflecting surface such as integrating sphere. The reflecting surface according to said method is obtained by repeatedly spraying a purified white paint onto a previously under coated surface to laminate the coating layers until a certain spectral reflectance and diffusibility are attained.
Such coating layer has relatively higher mechanical strength than the MgO smoked surface and can be used as a working reflecting surface. However, optical characteristics corresponding to those of the smoked surface can be obtained only with difficulty and only over a long period of time.
For example, at least 1 mm thickness of the coating layer is required to obtain a spectral reflectance of higher than 95% in visible area (relative value to the MgO smoked surface). However, as many as 30 - 40 spraying applications are required in view of the conditions of spray coating and the paint compositions and a considerably long coating period is necessary when drying time and the like are included. Furthermore, in many cases, the surface of the coating layer becomes rough or cracks are formed thereon, whereby the spectral reflectance and diffusibility are damaged. Furthermore, such coating layer changes with lapse of time due to temperature, humidity, radiation, dusts, etc. and it is difficult to maintain the original characteristics for a long period. Therefore, re-coating is necessary at regular intervals (generally, one time in 1 - 3 years) depending upon extent of deterioration.
A second problem is the trouble of dusts and loss of paint caused by spray coating.
Dispersion of paint in a large amount in the air during spray coating results in economical loss and contamination of air. Furthermore, it causes serious trouble to painters, other persons and to buildings, equipment, and so forth in which and around which the spray coating operation is accomplished. These troubles are especially serious in such coating conditions as in an integrating sphere. Therefore, extra exhaust apparatus and dust preventing equipment are required. Furthermore, during the coating, the surrounding buildings and equipment must be closed and in many cases, the usual business is prevented.